I'm looking to building my own circuit board based on the Arduino Mega 2560 and looked into their schematic. There are two micro-controllers on there; the ATMega2560 and the ATMega16U2. Both of them have their own 16MHz crystal. But their crystal is slightly different from each other.
The ATMega2560 is connected to this crystal with its built in capacitors with a load capacitance of 15pF. However, the ATMega16U2 is connected to a different crystal (load capacitance of 16pF) and requires external capacitors. The specs of the two are pretty much the same as far as I can see.
Would it not make sense to just use make both crystals the same model? Is there a reason as to why they are different? I looked at the price of both and they're about the same. Would my design still work if I just replaced the crystal on the 16U2 with the one on the 2560?
Crystal Schematic on the 2560
Crystal Schematic on the 16U2
Best Answer
The ATmega16U2 uses a quartz crystal because it needs a very accurate and stable frequency for USB. The ATmega2560 uses a ceramic resonator which is less accurate, but cheaper (lower unit cost, fewer parts, smaller board area).
If saving a few cents isn't important then you could use a quartz crystal for both MCUs. This would make your board more suitable for applications requiring high accuracy, eg. a real-time clock or frequency counter.